1. Field of the Invention
The present invention relates to a procedure for allocating the calls entered via landing call devices so that all calls will be served.
2. Description of Related Art
When a passenger wants to take an elevator from one floor of a building to another floor, he/she calls an elevator by pressing a landing call button mounted on their floor. The elevator control system receives the call and tries to determine which one of the elevators in the elevator bank will be best to serve the call. This operation is referred to as call allocation. The problem to be solved by allocation is to determining which one of the plurality of elevators will minimize a specified cost function. Allocation may involve minimizing passengers' waiting time, passengers' travelling time, the number of stoppages of the elevator or a combination of several cost factors of varying weight.
Conventionally, to establish which one of the elevators will be suited to serve a call, allocation is performed individually in each case by using complex condition structures. The ultimate aim of this operation is to minimize a cost factor describing the operation of the elevator group, typically the average waiting time for passengers. Since the elevator group has a complex variety of possible states, the condition structures are also complex and often have gaps. This leads to situations in which the control does not work in the best possible way. A typical example of this is the conventional collective control, in which each landing call is allocated to the one of the elevators which is currently closest to and moving toward the calling floor. However, this simple optimizing principle leads to an aggregation of the elevators, with the result being that the elevators travel together in the same direction, thereby deteriorating the performance of the elevator group as a whole.
When attempting to determine the cost factors of all possible alternative routes, the calculation load required may easily exceed the capacity of the processors. If the number of calls to be served is C and the building has L elevators, then the number of different alternative routes will be N=L.sup.C. As the number of alternative routes increases exponentially with the number of calls, it will be impossible, even in small elevator groups, to systematically analyze all the alternatives. This has limited the application of route optimization in practice.